1. Field of the Invention
The invention relates in general to fluid jet heads, and more particularly to fluid jet heads with driving circuit of a heater.
2. Description of the Related Art
Technological advancements have led to the wide use of fluid jet heads in application of inkjet heads of inkjet printers. Thermal driver bubbles, especially, are a commonly adapted method in inkjet head design for ejecting ink droplets. The reason for the wide use of inkjets using such method can be accredited to the simplicity in design, low production costs, and ability to separately output uniformly sized ink droplets.
FIG. 1 shows a bubble jet head having discharging mechanism according to U.S. Pat. No. 5,604,519, which includes a heater 102, a MOSFET 104, and a pull-down resistor 106. Heater 102 is electrically connected to the drain of MOSFET 104, and pull down resistor 105 is electrically connected to the gate of MOSFET 104. When MOSFET 104 goes from an on to an off state, the remaining charge left on the gate is discharged via resistor 106 to ground in specified periods. Thus, the error situations resulting from the continuing ejection of ink droplets from the corresponding nozzles in case of MOSFET turning off too late can be prevented.
However, in one embodiment of the U.S. Pat. No. 5,604,519, pull-down resistor 106 is a snake-shaped resistor formed by conducting materials. Between the snake-shaped resistor and the substrate, there exists a SiO2 insulation layer. Since pull-down resistor 106 does not come in direct contact with the substrate, which has a thermoconductivity of 160 W/mk, but rather forms direct contact with the SiO2 of thermoconductivity 1.4 W/mK. Thus, the disadvantage of the pull down resistor is that it is not very efficient in heat dissipation. Also, another disadvantage of inkjet head disclosed by U.S. Pat. No. 5,604,519 is that, due to the size of the snake-shaped resistor, large chip areas are needed to accommodate the size.
FIG. 2 shows a diagram of an inkjet head capable of producing same heat energy from every heater. Since each heater is positioned different in location, the length of the trace connecting to the two ends of every heater 56 is different. The parasitic resistance on the two ends of every heater 56 is thus different. This difference in parasitic resistance in turn causes the current flowing thought heater 56 to be different, and as a result, the heat energy produced by heater 56 is also different. Consequently, under U.S. Pat. No. 6,412,917, the parasitic resistance on two ends of each heater 56 is compensated through adjusting the channel width of MOSFET 85 cascaded under heater 56 (and thereby adjusting the channel resistance). However, the disadvantage of U.S. Pat. No. 6,412,917 is that the inkjet head is not equipped with the capability to discharge the charge remaining on the gate of the MOSFET
Thus, being able to design a fluid jet capable of effectively discharging the charge remaining in the gates of transistors to ground quickly in order to increase the fluid jet head operation speed, while compensating the parasitic resistances associated with the two ends of every heater is one of the goals that the industry has been trying hard to achieve.